A Thermokarst Lake (IMAGE) U.S. National Science Foundation Caption Thermokarst lakes occur as permafrost thaws and creates surface depressions that fill with melted freshwater. Credit Katey Walter Anthony / University of Alaska Fairbanks Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.